[....] Starting periodic command scheduler: cron[?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 12.579741] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 18.663926] random: sshd: uninitialized urandom read (32 bytes read) [ 18.901288] random: sshd: uninitialized urandom read (32 bytes read) [ 19.680499] random: sshd: uninitialized urandom read (32 bytes read) [ 39.125712] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.0.21' (ECDSA) to the list of known hosts. [ 44.535922] random: sshd: uninitialized urandom read (32 bytes read) executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program [ 45.197587] ================================================================== [ 45.205003] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 45.212266] Read of size 4 at addr ffff8801c122ec80 by task syz-executor091/3975 [ 45.219770] [ 45.221375] CPU: 1 PID: 3975 Comm: syz-executor091 Not tainted 4.9.103-g0cecdf8 #35 [ 45.229138] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 45.238465] ffff8801c2097b00 ffffffff81eb34a9 ffffea0007048b80 ffff8801c122ec80 [ 45.246487] 0000000000000000 ffff8801c122ec80 ffffffff83012be0 ffff8801c2097b38 [ 45.254470] ffffffff815676bb ffff8801c122ec80 0000000000000004 0000000000000000 [ 45.262504] Call Trace: [ 45.265072] [] dump_stack+0xc1/0x128 [ 45.270411] [] ? sock_release+0x1c0/0x1c0 [ 45.276186] [] print_address_description+0x6c/0x234 [ 45.282837] [] ? sock_release+0x1c0/0x1c0 [ 45.288605] [] kasan_report.cold.6+0x242/0x2fe [ 45.294817] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 45.301543] [] __asan_report_load4_noabort+0x14/0x20 [ 45.308267] [] l2tp_session_queue_purge+0xf4/0x100 [ 45.314826] [] ? sock_release+0x1c0/0x1c0 [ 45.320594] [] pppol2tp_release+0x1fb/0x2e0 [ 45.326535] [] sock_release+0x96/0x1c0 [ 45.332052] [] sock_close+0x16/0x20 [ 45.337302] [] __fput+0x263/0x700 [ 45.342375] [] ____fput+0x15/0x20 [ 45.347452] [] task_work_run+0x10c/0x180 [ 45.353136] [] do_exit+0x9e1/0x27c0 [ 45.358386] [] ? vm_insert_mixed+0x200/0x200 [ 45.364415] [] ? release_task.part.19+0x1210/0x1210 [ 45.371058] [] ? __do_page_fault+0x5dd/0xd50 [ 45.377087] [] ? up_read+0x1a/0x40 [ 45.382249] [] ? __do_page_fault+0x183/0xd50 [ 45.388277] [] do_group_exit+0x111/0x340 [ 45.393968] [] ? do_group_exit+0x340/0x340 [ 45.399839] [] SyS_exit_group+0x1d/0x20 [ 45.405436] [] do_syscall_64+0x1a6/0x490 [ 45.411136] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 45.418031] [ 45.419641] Allocated by task 3973: [ 45.423241] save_stack_trace+0x16/0x20 [ 45.427187] save_stack+0x43/0xd0 [ 45.430612] kasan_kmalloc+0xc7/0xe0 [ 45.434299] __kmalloc+0x11d/0x300 [ 45.437812] l2tp_session_create+0x38/0x16f0 [ 45.442190] pppol2tp_connect+0x10d7/0x18f0 [ 45.446485] SYSC_connect+0x1b8/0x300 [ 45.450256] SyS_connect+0x24/0x30 [ 45.453769] do_syscall_64+0x1a6/0x490 [ 45.457626] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 45.462705] [ 45.464303] Freed by task 3895: [ 45.467554] save_stack_trace+0x16/0x20 [ 45.471498] save_stack+0x43/0xd0 [ 45.474922] kasan_slab_free+0x72/0xc0 [ 45.478781] kfree+0xfb/0x310 [ 45.481858] l2tp_session_free+0x166/0x200 [ 45.486063] l2tp_tunnel_closeall+0x284/0x350 [ 45.490527] l2tp_udp_encap_destroy+0x87/0xe0 [ 45.494999] udpv6_destroy_sock+0xb1/0xd0 [ 45.499119] sk_common_release+0x6d/0x300 [ 45.503249] udp_lib_close+0x15/0x20 [ 45.506948] inet_release+0xff/0x1d0 [ 45.510636] inet6_release+0x50/0x70 [ 45.514333] sock_release+0x96/0x1c0 [ 45.518016] sock_close+0x16/0x20 [ 45.521444] __fput+0x263/0x700 [ 45.524695] ____fput+0x15/0x20 [ 45.527948] task_work_run+0x10c/0x180 [ 45.531813] do_exit+0x9e1/0x27c0 [ 45.535239] do_group_exit+0x111/0x340 [ 45.539096] SyS_exit_group+0x1d/0x20 [ 45.542949] do_syscall_64+0x1a6/0x490 [ 45.546822] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 45.551892] [ 45.553494] The buggy address belongs to the object at ffff8801c122ec80 [ 45.553494] which belongs to the cache kmalloc-512 of size 512 [ 45.566121] The buggy address is located 0 bytes inside of [ 45.566121] 512-byte region [ffff8801c122ec80, ffff8801c122ee80) [ 45.577791] The buggy address belongs to the page: [ 45.582692] page:ffffea0007048b80 count:1 mapcount:0 mapping: (null) index:0xffff8801c122f400 compound_mapcount: 0 [ 45.594165] flags: 0x8000000000004080(slab|head) [ 45.598886] page dumped because: kasan: bad access detected [ 45.604568] [ 45.606166] Memory state around the buggy address: [ 45.611067] ffff8801c122eb80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 45.618397] ffff8801c122ec00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 45.625727] >ffff8801c122ec80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 45.633055] ^ [ 45.636391] ffff8801c122ed00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb executing program executing program executing program [ 45.643720] ffff8801c122ed80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 45.651048] ================================================================== [ 45.658377] Disabling lock debugging due to kernel taint [ 45.666615] Kernel panic - not syncing: panic_on_warn set ... [ 45.666615] [ 45.673978] CPU: 1 PID: 3975 Comm: syz-executor091 Tainted: G B 4.9.103-g0cecdf8 #35 [ 45.682959] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 45.692296] ffff8801c2097a60 ffffffff81eb34a9 ffffffff843c5d75 00000000ffffffff [ 45.700301] 0000000000000000 0000000000000001 ffffffff83012be0 ffff8801c2097b20 [ 45.708291] ffffffff81421aa5 0000000041b58ab3 ffffffff843b94a8 ffffffff814218e6 [ 45.716302] Call Trace: [ 45.718868] [] dump_stack+0xc1/0x128 [ 45.724205] [] ? sock_release+0x1c0/0x1c0 [ 45.729986] [] panic+0x1bf/0x3bc [ 45.734975] [] ? add_taint.cold.6+0x16/0x16 [ 45.740928] [] ? ___preempt_schedule+0x16/0x18 [ 45.747134] [] kasan_end_report+0x47/0x4f [ 45.752904] [] kasan_report.cold.6+0x76/0x2fe [ 45.759023] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 45.765761] [] __asan_report_load4_noabort+0x14/0x20 [ 45.772483] [] l2tp_session_queue_purge+0xf4/0x100 [ 45.779032] [] ? sock_release+0x1c0/0x1c0 [ 45.784802] [] pppol2tp_release+0x1fb/0x2e0 [ 45.790744] [] sock_release+0x96/0x1c0 [ 45.796255] [] sock_close+0x16/0x20 [ 45.801512] [] __fput+0x263/0x700 [ 45.806587] [] ____fput+0x15/0x20 [ 45.811672] [] task_work_run+0x10c/0x180 [ 45.817355] [] do_exit+0x9e1/0x27c0 [ 45.822601] [] ? vm_insert_mixed+0x200/0x200 [ 45.828629] [] ? release_task.part.19+0x1210/0x1210 [ 45.835267] [] ? __do_page_fault+0x5dd/0xd50 [ 45.841297] [] ? up_read+0x1a/0x40 [ 45.846458] [] ? __do_page_fault+0x183/0xd50 [ 45.852485] [] do_group_exit+0x111/0x340 [ 45.858165] [] ? do_group_exit+0x340/0x340 [ 45.864018] [] SyS_exit_group+0x1d/0x20 [ 45.869615] [] do_syscall_64+0x1a6/0x490 [ 45.875299] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 45.882605] Dumping ftrace buffer: [ 45.886128] (ftrace buffer empty) [ 45.889820] Kernel Offset: disabled [ 45.893430] Rebooting in 86400 seconds..